The present invention relates to signal processing, and more particularly to echo cancellation devices and methods.
Hands-free telephones (e.g., speakerphones) provide conveniences such as conversations while driving an automobile and teleconferencing with multiple speakers at a single phone. However, acoustic reflections of the loudspeaker output of a hands-free phone to its microphone input simulate another participant speaker and thus appear as an echo to the original remote speaker. Acoustic echo cancellation and echo suppression attempt to minimize these effects.
Acoustic echo cancellation (AEC) methods approximate the properties of the loudspeaker-to-microphone acoustic channel and thereby can generate an approximation of the microphone pickup of sounds emitted by the loudspeaker. Then this approximation can be cancelled from the actual microphone pickup. Acoustic echo cancellation typically uses adaptive filtering to track the varying acoustic channel; see U.S. Pat. No. 5,633,936. FIGS. 2a-2b illustrate the acoustic channel and the adaptive filter. Such a system requires fast filter convergence as the acoustic channel varies and separation of the echo from near-end sources such as speech or noise.
Various methods for filter definition and fast convergence have been proposed, including normalized least mean squares with input decorrelation or affine projection. See for example, Doherty et al, A Robust Echo Canceler for Acoustic Environments, 44 IEEE Trans. Circuits Systems 389 (1997) and Dutweiler, Proportionate Normalized Least-Mean-Squares Adaptation in Echo Cancellers, 8 IEEE Tran. Speech Audio Proc. 508 (2000).
However, these approaches still have problems of insufficient performance.